1 | customer development and application eng. | 31/07/2015 · 7 | customer development and...

1 | Customer Development and Application Eng. | 31/07/2015

Wireless Transmission

A Fundamental Guide . . .

Joe Ciaudellie/ Spectrum Affairs

Volker Schmitt / Customer Development and Application Engineering


Agenda

RF Spectrum

Digital Audio Transmission


Recent FCC Rulings

Changes In Spectrum Policy The Impact On Wireless Mic Operations Joe Ciaudelli

Spectrum Crunch


Frequencies for Wireless Mic´s

30 - 45 MHz (8-m HF)

174 - 250 MHz (VHF)

450 - 960 MHz (UHF)

2400 - 2485 MHz (ISM) IndustrialScientificMedical

Antenna length ;

RF-interference from (electric) appliances

Good wave propagation; TV-transmitters;

RF-distortions from digital equipment

wide frequency range

good wave propagation

poor wave propagation ;

no exclusive frequencies

(license free devices);

interference from microwave-ovens

6 | Customer Development and Application Eng. | 31/07/2015 6 |

UHF has greater range

compared to higher

frequencies

500 MHz UHF frequency

(green line) requires

only about 75 mW to

transmit 1 kilometer

(about ½ mile) – line of

sight.

2.4 GHz (red line) requires

about 1000 mW (much

greater power) to travel

the same distance

Range / Power / Frequency

Receiver-Ant.

U= 100 µV

Dist. (km) Power Att. (dB) Freq.


UHF is the beach front property in the spectrum

Provides exceptional wave propagation characteristics

Travels through foliage, walls, furniture, etc

Operates with compact antennas and filter components

Important for small mobile transmitters like mics

Less susceptible to noise from electronic devices

Long transmission range using moderate power output


Operating in vacant (“white space”) TV channels

DTV Signal DTV Signal

Ch. 20 Ch. 21 Ch. 22 Ch. 23 Ch. 24

Wireless Mics

50 mW

DTV Signal DTV Signal


UHF TV frequencies

TV Transmitter Wireless microphones

~20 years ago:

Analog TV only

470 MHz 806 MHz CH14 CH69

2010

Digital Dividend

New Services

UHF TV frequencies 2010

Now:

Full Digital Scenario

DTV Transmitter

Transition:

Analog & DTV

DTV Transmitter

Broadband 2018?

Digital Dividend

New Services

UHF TV frequencies 2018?

Future:

More Broadband services

DTV Transmitter

New Incentive

Auction


What You Should Know

A large portion of the upper UHF spectrum, specifically the 600 MHz band will be

repurposed and become unavailable to mics in about three (3) years in the United

States.

There will be small pockets in the repurposed spectrum where mics will still be

allowed to operate, under different rules, after the spectrum repacking is completed.

License eligibility has been expanded, providing valuable rights to additional

categories of wireless mic professionals.

Rules regarding co-channel operation with TV broadcast have been revised, opening

some channels to mics at locations that were formerly prohibited.

Additional frequency bands outside of UHF are likely to become available to wireless

mics in the future.

Spectrum sharing with other devices and services will be “the new norm”


Licensed vs Unlicensed Mic Operation

Licensed

Priority over unlicensed operation

Operate up to 250mW in UHF band.

Unlicensed

Limited to 50mW

No recourse if interference is experienced.

- Consumer alert at point-of-sale or packaging


License Eligibility

.

Previously only broadcasters, cable TV operators, film

and content providers were eligible to obtain a license.

Now sound companies and venues who routinely use 50

mics are too.


“White Space” channels 2 – 51 are open to unlicensed devices:

Rural broadband internet

Metropolitan broadband internet

Multimedia services

Home networking systems

Consumer electronics: PDA’s and cell phones w/ advanced features

Future products

White Space Devices (WSD) a.k.a. TV White Space (TVWS) or TV Band Devices (TVBD)


White Space Devices - WSD

A new class of consumer electronics operating in the TV spectrum on

locally vacant channels. They are categorized as:

Fixed

Moderate power: up to 4W

A few are currently active – mostly on school campuses

Personal/Portable

Low power: 40 – 100 mW (like wireless mics)

Not in the market yet


Safeguards For Wireless Mics

FCC rules governing WSD include safeguards to avoid interference

to wireless microphones:

Reserved channels: 2 channels in each market are reserved for

wireless mics – but the FCC plans to eliminate them !

WSD must use Geolocation/Database system to find channels that

are not reserved for TV or by wireless mic operators


Database System

Licensed mic operators have direct access to reserve additional channels


Wireless Microphone Protection Area

400m protection from mobile

WSDs

1 km protection from fixed

WSDs

May specify up to 25

geographic points per

registration

Microphone operating around

a geographic point


Wireless Microphone Protection Area, cont’d.


WSDs


WSDs



registration

Protection of composite area


a geographic point




WSDs


WSDs


a geographic point



registration

Protection of composite area



Microphone operating area - 3

km square

May specify up to 4 polygons

per registration


WSDs


WSDs

Polygon – limited to

4 vertices & 3 km sides


Incentive Auction

Two Parts:

Reverse Auction

TV stations can voluntarily participate in return for a portion of the auction revenues. They can opt to:

Go off the air

Share a channel with another station

They privately indicate their minimum price to the FCC. Their spectrum then becomes available in the:

Forward Auction

Wireless broadband providers can then bid on the spectrum available in the various markets.

22 | Customer Development and Application Eng. | 31/07/2015 22 |

Current TV band

TVWS devices are

presently few and far

between

Distant / low field strength TV signal:

co-channel operation possible

Full power TV Exclusive mic

channels

Ch 14 Ch 37 Ch 51

Shared white

space channel

Repacking scenario

(simplified)

7 station off air

4 stations relocated

Downlink Uplink

Guard band:

unlicensed

operation of

mics & WSD

Duplex Gap

for licensed

mic use. High

noise floor

possible

Duplex Gap

unlicensed

operation of

mics & WSD

Naturally occurring White Space

channel. Higher activity as more

TVWS devices enter the market


Long Term Future

The FCC has stated its commitment "...to accommodate the

longer-term needs of wireless microphone users through use

of additional frequency bands to meet their varying needs.“

In discussion:

941-960 MHz (licensed only)

1435-1525 MHz (licensed only)

2020-2025 MHz


Ready . . . Steady . . . Digital


Advantages of Digital Audio Transmission

No/ less compromises in audio quality

( without audio codec)

Even with audio codec usually better audio quality compared

to compander systems

Encryption of the transmission link

Spectral efficiency can be further increased

If you are doing it the right way!


Challenges of Digital Audio Transmission

Latency

Operating time, size

Higher cost

Missing experience (at this point in time)



No data compression

Improved sound quality

Less artifacts

High data rate

Complex Digital Modulation Scheme Less Robust RF Transmission

Due to Higher Carrier/ Noise Ratio

High Power Dissipation

Less battery life time

Linear RF Amplifier

Ref -0.5 dBm Att 20 dB*

*

*

*1 RM

MAXH

A

RBW 1 kHz

VBW 1 kHz

SWT 1.5 s

Center 800 MHz Span 1.5 MHz150 kHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

AKSENSHU

Date: 25.NOV.2010 12:10:57

High RF bandwidth


Modulation


Difference in Modulation

There are three characteristics of a carrier

Amplitude

Phase/ Frequency

Digital Modulation is a misnomer and refers to an analog carrier

modulated with digital data


No Audio Data Compression results in high data rate

24Bit * 96kHz ≈ 2.3MBit/s

Additional Data for Framing and

Channel Coding (usually x1,5)

3.4MBit/s

24Bit, 96kHz

How much Data Rate is Required?


Constellation Diagrams

Low complexity Modulation Schemes (FSK, PSK, ASK)

provide only a fraction of the needed Data Rate

(within 200kHz RF Bandwidth typ. 150kBit/s…300kBit/s)

FSK

1 bit / symbol

QAM

2 bits / symbol


Constellation Diagrams

Order of modulation increases,

the number of constellation points increases

4 bits/symbol (24 CPs) 5 bits/symbol (25 CPs) 6 bits/symbol (26 CPs)


Narrow RF channel bandwidth of 200kHz (ETSI EN300422)

Higher Data Rate requires

High CNR/CIR

Physical Limit

Feasible today

Channel Capacity (BER=10^-3)

CNR/CIR [dB]

How does it Work – Digital Transmission?


Difference between Analogue and Digital Transmission


Digital Links behave different to FM Links

FM: Audio SNR depending on receiving field strength

Digital: Direct changeover from Muting to superior audio

FM:

Graceful Degradation

Digital

-110dBm -100dBm -90dBm

RFin [dBm]

Au

dio

SN

R

Audio SNR vs. RF level

(schematically)


YOU THANK

Q&A

1 | customer development and application eng. | 31/07/2015 · 7 | customer development and...

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